In modern aircraft, it is desirable to integrate, as far as possible, the functions of previously-independent avionic systems to permit an attendant reduction in weight, space and power requirements of the avionic systems and a simplification in wiring between physically separated avionic systems or subsystems thereof. Such integration has been achieved by the use of a common data communication medium, or data bus, to which each avionic system, or subsystem thereof, has access through an associated terminal, each of which is capable of transmitting and receiving data on the data bus. Data transmitted on the data bus by one terminal associated with a particular system or subsystem can be received by the terminals associated with the remaining systems or subsystems, thus eliminating the requirement for separate wiring interconnections between the systems or subsystems. In addition, data generated in a particular system or subsystem can be used by any other system or subsystem without the necessity of having to independently generate that data.
In order for a data communication system using a data bus to properly and reliably operate, without degradation upon the performance of any of the systems or subsystems coupled thereto, it is desirable that the data communication system allow tranmission of data originating from any terminal to any or all of the remaining terminals using a minimum physical length of the data bus. Also, the data communication system must be capable of accommodating periodic tranmission of any or all data. For example, if a particular terminal is inhibited from transmitting in a periodic manner, then those terminals that depend upon such data may malfunction. Further, operation of any one of the systems, subsystems or terminals associated therewith, must not be affected by the operational status of any other system, subsystem or terminal, whether such other system, subsystem or terminal be operating normally or be malfunctioning. Finally, the data bus, and any devices for coupling the data bus to each terminal which conceivably could render the data bus unusable, must be of such high functional integrity so as to make the possibility of data bus failure extremely remote.
The data communication systems using a data bus that have been particularly proposed for use in aircraft have taken two forms. The first, known as a broadcast bus, includes a single data bus which is exclusively assigned to one data source terminal. Data transmitted on the data bus from the data source terminal can be received by any number of receiver terminals coupled to the data bus. Although the broadcast bus is capable of accommodating periodic data transmissions, it is not capable of bilateral data communications. Accordingly, a separate data bus must be used for each data source terminal. Also, any device requiring the use of data from more than one data source terminal must be separately coupled with each required data bus. Accordingly, the broadcast bus does not permit a significant reduction to be made in aircraft wiring interconnections.
The second, known as a multiplex bus using a central bus controller, includes a single data bus having coupled thereto a plurality of remote terminals and a central bus controller terminal. The bus controller terminal determines (under software control) the mode of operation of any remote terminal, and controls such mode of operation by the transmission of command words on the bus. The multiplex bus, although capable of significantly reducing aircraft wiring interconnections, is not inherently suitable for periodic data transmission by each remote terminal. More important, the operation of remote terminals is not autonomous due to their dependence on the bus controller terminal, so that failure of the bus controller terminal constitutes failure of all remote terminals associated with the data bus.
It is therefore an object of this invention to provide an improved data communication system using a data bus.
It is a further object of this invention to provide such a data communication system which permits each participating terminal to have autonomous access to the data bus.
It is yet a further object of this invention to provide such a data communication system in which normal operation of any participating terminal, or malfunction thereof, will not affect the operation of the data communication system or of any other participating terminal associated therewith.
It is another object of this invention to provide such a data communication system which permits each participating terminal to engage in periodic data tranmissions on the data bus.
It is yet another object of this invention to provide such a data communication system which affords multiplexed data communications among participating terminals without the requirement for a central bus controller terminal.
It is still another object of this invention to provide such a data communication system which permits a significant reduction in the wiring requirements between participating systems and a significant increase in the integration of such systems.